Process for continuously producing aluminum from clays

ABSTRACT

A process for continuous production of metal chlorides includes the steps of providing metallic ore, containing iron purities, and a carbon source; drying the metallic ore; drying the carbon source; mixing the dried metallic ore, the dried- carbon source, and a sulfur-containing compound; calcining the mixture in a first fluidized bed reactor in the presence of air; chlorinating the calcined product in a second fluidized bed reactor in the presence of additional carbon source and additional sulfur-containing compound to produce crude metal chlorides and waste gases; and reactively subliming and desubliming the crude metal chlorides, in the presence of additional iron, aluminum, cesium, copper, lead, lithium, magnesium, mercury, potassium, sodium, titanium, uranium, zinc or zirconium, to produce purified aluminum chloride.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a divisional of co-pending U.S. patent application Ser.No. 09/576,368, which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED OR DEVELOPMENT

[0002] None

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates to pyrometallurgical processing,including a process for producing aluminum metal and titaniumtetrachloride from clays containing hydrous aluminum silicate andtitanium. More particularly, the present invention relates to a processfor improving yield in removing iron in the purification of aluminumchloride through the addition of iron particles or equivalent ironcontaining compounds. The reactive sublimation of impure aluminumchloride with a reducing agent of iron in finely divided formsubstantially purifies the impure aluminum chloride. The purifiedaluminum chloride can then be effectively smelted into aluminum byaluminum chloride smelting processes.

[0005] 2. Description of Related Art

[0006] For over one hundred years, a customary method of producingaluminum commercially has been the well-known Hall-Heroult process inwhich alumina dissolved in a fluoride bath (principally cryolite) isreduced electrolytically. The Hall-Heroult process requires a feed ofpure alumina, which is typically produced commercially by the Bayerprocess, which in turn requires a feedstock of high grade bauxite.Bauxite occurs in few areas of the world, and no commercial depositsexist in North America.

[0007] Production of aluminum by electrolysis of aluminum chloridedissolved in a molten electrolyte composed of one or more halides havinghigher electrodecomposition potential than aluminum chloride (e.g.,alkali metal halide or alkali earth metal halide) has been described inthe literature; for example, Z. fur Elektrochemie, Vol. 54, pp. 210-215,U.S. Pat. Nos. 1,296,575, 1,854,684, 2,919,234, 3,103,472, 3,725,222 andCanadian Patent No. 502,977. This aluminum chloride smelting wasinitially thought to promise higher energy efficiency than theBayer-Hall-Heroult process, but the promise went unrealized commerciallybecause of problems and costs related to impurities in the aluminumchloride.

[0008] Purity of aluminum chloride feedstock is deemed essential tosuccessful commercial production of aluminum by electrolysis of thealuminum chloride in a molten electrolyte. U.S. Pat. No. 3,725,2222,assigned to Alcoa, disclosed that it is highly important that theconcentration of metal oxides in the bath, expressed as oxygen, be keptbelow 0.25 percent by weight, and preferably below 0.1 percent byweight, and more preferably, below 0.05 percent. Alcoa's smeltingprocess utilized Bayer alumina that was chlorinated by first sprayingfuel oil onto hot alumina particles, which pyrolized the oil intoreactive carbon deposited on the alumina particle surfaces, and thenreacting the carbonized aluminum with chlorine. Alcoa did not usealuminum chloride from low grade clays.

[0009] Production of purified aluminum chloride from low grade aluminousmaterials, including kaolin clays, bauxites, aluminum phosphate, shaleand other raw materials by a carbo-chlorination process, followed byoxidation of the purified aluminum chloride into high grade aluminumoxide is disclosed in U.S. Pat. Nos. 3,935,297, 3,937,786, 3,938,969,3,950,485, 3,956,454, 4,035,169, 4,082,833, 4,083,923, 4,083,927,4,203,962, 4,220, 629, 4,514, 373, 4,695,436, and 4,710,369. Thisprocess of carbo-chlorination was directed to replacing bauxite-basedaluminum oxide with aluminum oxide produced by the oxidation of purifiedaluminum chloride. For example, U.S. Pat. Nos. 4,514,373 and 4,695,436disclose a process for producing substantially pure aluminum chloride bysubliming and desubliming solid crude metal chlorides, which have beencombined with aluminum powder. The other metal chlorides are separatedfrom the aluminum chloride. But this process is less cost effectivebecause of the cost of aluminum powder. Also, any excess aluminum powderis not easily or cost effectively recoverable.

[0010] Accordingly, it is an object of the present invention to providea more cost effective process for purifying aluminum chloride. It isfurther object of the invention to improve the production of purifiedaluminum chloride for use in the production of aluminum by electrolysisof aluminum chloride.

[0011] It is another object of the invention to provide a continuousprocess for producing aluminum from low grade aluminous materials.

[0012] It is yet another object of this invention to provide a processfor obtaining titanium tetrachloride and silicon tetrachloride from lowgrade aluminous materials containing titania and silica.

[0013] These and other objects will be apparent from the description ofthe invention and the claims, taken in conjunction with the drawing, orby practice of the invention.

SUMMARY OF THE PRESENT INVENTION

[0014] What is provided is a process in which aluminous ore, a carbonsource, and other raw materials are used to make and purify aluminumchloride, titanium tetrachloride, and silicon tetrachloride. Ores usablein this invention are those containing aluminum oxides and silicatesthat may be carbo-chlorinated using the instant catalyst at atemperature range of approximately 500° C. to approximately 1000° C.Examples of such ores include kaolinitic, illitic, and other aluminumclays; bauxite clay and other bauxite ores; siliceous bauxites andsillimanites; kyanites; aluminous shale, slates and fuel ashes;nepheline syenites; and anorthosite. The carbon source which is used inthe drying process may be a carbonaceous gas such as carbon monoxide orcarbonyl chloride or phosgene, or it may be one of a number of coalcokes or chars, including cokes and chars from lignite, petroleum cokeand peat. The process is generally comprised of the following steps:

[0015] Step 1—Drying

[0016] The aluminous ore is fed into a dryer where it is dried with offgases from a calciner at a temperature range between approximately 100°C. and 200° C. The dryer removes the free water from the aluminous ore.The carbon source is fed to a dryer where it is dried under controlledatmosphere, low in oxygen, between approximately 100° C. and 150° C.

[0017] Step 2—Calcination

[0018] The pyrometallurgical calcination step utilizes elevatedtemperatures to remove the chemically bound water from the aluminous oreat a temperature of between 600° C. and 950° C. The ore must be driedand removed of free water and chemically bound water to preventobjectionable hydrolysis of metal chlorides or the formation ofcorrosive hydrochloric acid.

[0019] Step 3—Chlorination

[0020] During the chlorination step, a chlorinating agent such as drychlorine gas and/or a functionally equivalent chlorine compound iscombined with the ore, catalyst, and reductant, at elevated temperatureof 600° C. to 1000° C.

[0021] Step 4—Condensation

[0022] The solids condensation system receives the hot vapors from thechlorinator and recovers heat and condenses crude, impure aluminumchloride. A heat exchanger and aluminum chloride condenser are used tothe solids condensation system.

[0023] Step 5—Liquids Condensation

[0024] The uncondensed vapors from the solids condensation unit flowinto the liquids condensation system for condensation of approximately98% of the silicon tetrachloride and 98% of the titanium tetrachloride.

[0025] Step 6—Silicon Tetrachloride and Titanium TetrachloridePurification

[0026] The liquid mixture recovered in Step 5 is directed toconventional rectification and condensation equipment for separation ofthe silicon tetrachloride and titanium tetrachloride and furtherpurification of silicon tetrachloride and titanium tetrachloride.

[0027] Step 7—Aluminum Chloride Purification (Blender)

[0028] During the blending operation, the crude solid aluminum chloridecompound and powdered metal, preferably iron at the feed rate of 1-5molar relative to the metal impurity level in the crude aluminumchloride, are fed into a blender.

[0029] Step 8—Multi-State Sublimation

[0030] A first sublimer commonly used in sublimation processes receivesthe mixture from the blender and, operating at a temperature of at least180° C. and a pressure of at least one atmosphere, the solid aluminumchloride sublimes to aluminum chloride vapor at these conditions. Thesesteps of sublimation and desublimation are repeated until high purityaluminum chloride is achieved.

[0031] Step 9—Granulated Metal Reactor

[0032] The pure aluminum chloride from the sublimer may be directedthrough a granulated metal reactor where is comprised of solid granulesor activated granular metal which removes the sulfur impurities andnon-aluminum metal chloride traces.

[0033] Step 10—Aluminum Chloride Condenser

[0034] The purified aluminum chloride vapor/nitrogen mixture is thendirected into the condenser where the aluminum chloride solidifies at atemperature between 40° C. and 180° C.

[0035] Step 11—Aluminum Chloride Smelting

[0036] The purified solid aluminum chloride is then directed to closedsmelting cells where the aluminum chloride is dissolved in a moltenelectrolyte comprised of one or more halides having higherelectrodecomposition potential than aluminium chloride and is convertedby electrolysis into aluminum metal and chlorine.

[0037] Step 12—Chlorine Recovery

[0038] Chlorine from the electrolysis cells is cooled, compressed,liquefied and stored for recycle to the second fluidized bed reactor.

[0039] Step 13—Pollution Control

[0040] The pollution control system scrubs the waste gases from thesystem with an alkali solution before they are released to theatmosphere, where they then contain mostly carbon dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041]FIG. 1 is a block diagram illustrating the production of aluminummetal and titanium tetrachloride from clay, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0042] In the production of substantially pure aluminum chloride inaccordance with this invention, aluminum chloride containing ironimpurities is combined with additional iron in finely divided form, andthe resulting mixture is reactively sublimed and desublimed in asequence of heated reactors. Preferably, the additional iron is added ata rate of 1-5 molar relative to the metal impurity level in the crudealuminum chloride. When impure aluminum chloride containing up toapproximately 20% by weight of ferric chloride is reactively sublimed,the finely divided iron acts as a reducing agent to reduce the valencestate of iron from valence state III (ferric) to valence state II(ferrous). The resulting ferrous chloride has a substantially lowervapor pressure at the temperature of sublimation of aluminum chloride.The lower vapor pressure retards the evaporation of iron into thevaporous aluminum chloride, thereby achieving a sequential, stage-wisedecrease of iron in aluminum chloride. The additional iron is added ateach stage. After each reaction stage, the impurity level of iron in thealuminum chloride decreases. The number of such stages can be selectedto achieve a final desired purity level. For example, after three suchstages, in which the sublimed aluminum chloride vapor is reacted inthree sequential reactors containing iron particles, and held at atemperature of between 300° C. and 500° C., the iron content of theresultant aluminum chloride is reduced to about 20 parts per million.

[0043] The purification process also includes condensing liquid titaniumtetrachloride and silicon tetrachloride from the metal chlorides. Thetitanium tetrachloride can be recovered, purified and sold, and chlorinecan be recovered from the silicon tetrachloride and recycled to thechlorination process.

[0044] In the improved process according to the invention, aluminous oredried to about 5% moisture and a carbon source dried to about 1%moisture are mixed with a sulfur-containing compound, the mixture iscalcined in a first fluidized bed reactor in the presence of air at atemperature between about 600° C. and about 900° C., the calcinedproduct is chlorinated in a second fluidized bed reactor at atemperature between about 700° C. and about 1000° C. in the presence ofadditional carbon source and additional sulfur-containing compound toproduce crude metal chlorides and waste gasses, and the crude metalchlorides are reactively sublimed and desublimed in the presence offinely divided iron within a temperature range of between about 180° C.and about 350° C. and at a pressure of one atmosphere, the subliming anddesubliming being repeated in multiple stages to achieve a desiredpurity of aluminum chloride. Excess iron particles additionally can berecovered by a magnetic separation process.

[0045] The aluminum chloride vapor is passed through a series ofreactors, packed with iron particles, at a temperature of between about200° C. and about 500° C. Using finely divided iron as a reducing agentto separate iron chloride from the aluminum chloride is useful forpurifying low grade aluminous materials, for providing substantiallypure aluminum chloride for aluminum smelting, and for providing acontinuous process for producing aluminum from low grade aluminousclays.

[0046] The invention is not limited to the particular example disclosedherein.

[0047] More generally, virtually all metals, not only aluminum, can bechlorinated to yield their metal chlorides. The group that appears mostsusceptible to chloride based separation recovery and purificationaccording to the invention include the following: aluminum, antimony,arsenic, beryllium, bismuth, boron, cadmium, cerium, chromium, cobalt,copper, gallium, germanium, gold, hafnium, holmium, indium, iridium,iron, lead, lithium, magnesium, manganese, mercury, molybdenum, nickel,niobium, osmium, palladium, phosphorus, platinum, ruthenium, samarium,scandium, selenium, silicon, tantalum, tellurium, terbium, thallium,thulium, tin, titanium, tungsten, uranium, vanadium, zinc and zirconium.The metal chlorides of this group of metals are referred as Chaplinmetal chlorides. The group is referred to as the Chaplin metal chloridegroup.

[0048] Moreover, metals other than iron that act similar to iron in thereduction of ferric chloride to ferrous chloride can be used in thereactive sublimation step. Such reducing metals, preferably inparticulate or finely divided form, include the following: aluminum,cesium, copper, lead, lithium, magnesium, mercury, potassium, sodium,titanium, uranium, zinc and zirconium. These are referred to as Chaplinmetals. The group of these metals is referred to as the Chaplin metalgroup.

I claim:
 1. In a process for continuous production of aluminum byelectrolysis of aluminum chloride dissolved in a molten solvent having ahigher electrodecomposition potential than aluminum chloride, animprovement comprising: the aluminum chloride being substantially purealuminum chloride produced by a process comprising reactively sublimingand desubliming iron containing crude aluminum chloride in the presenceof additional iron.
 2. The improvement according to claim 1, wherein themolten solvent consists essentially of at least one salt selected fromthe group consisting of alkali metal chlorides and alkaline earth metalchlorides.
 3. The improvement according to claim 2, wherein the at leastone salt comprises of a molten salt mixture comprising two or more saltsselected from the group consisting of sodium chloride, lithium chloride,calcium chloride and strontium chloride.
 4. A process for continuousproduction of aluminum from aluminous ore, the process comprising thesteps of: (a) providing aluminous ore, containing iron impurities, and acarbon source; (b) drying the aluminous ore; (c) drying the carbonsource; (d) mixing the dried aluminous ore, the dried carbon source, anda sulfur containing compound; (e) calcining the mixture in a firstfluidized bed reactor in the presence of air; (f) chlorinating thecalcined mixture in a second fluidized bed reactor in the presence ofadditional carbon source and additional sulfur therein producing crudemetal chlorides and waste gasses; (g) condensing solid crude aluminumchloride and separating the solid crude aluminum chloride from gaseouscrude silicon tetrachloride and titanium tetrachloride; (h) reactivelysubliming and desubliming the solid crude aluminum chloride in thepresence of additional iron to produce substantially pure aluminumchloride; and (i) electrolysis of the substantially pure aluminumchloride dissolved in a molten solvent having a higherelectrodecomposition potential than aluminum chloride to producealuminum and chlorine.
 5. The process according to claim 4, furthercomprising: (a) condensing a mixture of liquid titanium tetrachlorideand liquid silicon tetrachloride from the waste gasses by cooling thewaste gasses; (b) separating the liquid mixture from the waste gasses;(c) distilling the liquid mixture to produce substantially pure titaniumtetrachloride and substantially pure silicon tetrachloride; and (d)recovering chlorine from a portion of the silicon tetrachloride andrecycling the chlorine to the second fluidized bed reactor.
 6. Theprocess according to claim 4, further comprising: recycling the chlorineto the second fluidized bed reactor.
 7. A process for continuousproduction of metal from metallic ore, the process comprising the stepsof: (a) providing metallic ore, containing iron impurities, and a carbonsource; (b) drying the metallic ore; (c) drying the carbon source; (d)mixing the dried metallic ore, the dried carbon source, and a sulfurcontaining compound; (e) calcining the mixture in a first fluidized bedreactor in the presence of air; (f) chlorinating the calcined mixture ina second fluidized bed reactor in the presence of additional carbonsource and additional sulfur, thereby producing crude metal chloridesand waste gasses; (g) condensing solid crude metal chloride andseparating the solid crude the metal chloride from gaseous crude silicontetrachloride and titanium tetrachloride; (h) reactively subliming anddesubliming the solid crude metal chloride in the presence of Chaplinmetal particles to produce substantially pure aluminum chloride; and (i)electrolysis of the substantially pure metal chloride dissolved in amolten solvent having a higher electrodecomposition potential than themetal chloride to produce metal and chlorine.
 8. In a process forcontinuous production of metal by electrolysis of a Chaplin metalchloride dissolved in a molten solvent having a higherelectrodecomposition potential than the Chaplin metal chloride, animprovement comprising: the Chaplin metal chloride being substantiallypure Chaplin metal chloride produced by a process comprising reactivelysubliming and desubliming a Chaplin-metal containing crude metalchloride in the presence of Chaplin metal particles.
 9. A process forcontinuous production of metal from metallic ore, the process comprisingthe steps of: (a) providing metallic ore, containing iron impurities,and a carbon source; (b) drying the metallic ore; (c) mixing the driedmetallic ore, the dried carbon source, and a sulfur containing compound;(d) mixing the dried metallic ore, the dried carbon source, and a sulfurcontained compound; (e) calcining the mixture in a first fluidized bedreactor in the presence of air; (f) chlorinating the calcined mixture ina second fluidized bed reactor in the presence of additional carbonsource and additional sulfur, thereby producing crude metal chloridesand waste gasses; (g) condensing solid crude metal chloride andseparating the solid crude metal chloride from gaseous crude silicontetrachloride and titanium tetrachloride; (h) reactively subliming anddesubliming the solid crude metal chloride in the presence of Chaplinmetal particles (i) electrolysis of the substantially pure metalchloride dissolved in a molten solvent having a higherelectrodecomposition potential than the metal chloride to produce metaland chlorine; (j) recycling the chlorine to the second fluidized bedreactor.